Binary cis-1,4-/1,2-polybutadiene is a polybutadiene rubber that has a microstructure in which the polymeric main chain consists almost exclusively of cis-1,4- and 1,2-units with almost no trans-1,4-units. Binary cis-1,4-/1,2-polybutadiene exhibits unique viscoelastic properties as compared to other synthetic rubbers. For instance, binary cis-1,4-/1,2-polybutadiene has higher green strength and higher tack than the polybutadiene having similar 1,2-linkage content that is made by anionic polymerization. Therefore, binary cis-1,4-/1,2-polybutadiene can be utilized in a variety of applications and is particularly useful as a tire rubber. It can also be blended into other synthetic rubbers and co-cured therewith.
Binary cis-1,4-/1,2-polybutadiene cannot be produced by anionic polymerization utilizing alkyllithium initiators. Only a few coordination catalyst systems based on transition metals are known for the preparation of binary cis-1,4-/1,2-polybutadiene. For example, Polymer Journal, Volume 2, page 371 (1971) discloses a process for polymerizing 1,3-butadiene into binary cis-1,4-/1,2-polybutadiene by using a catalyst system comprising cobalt tris(acetylacetonate), triethylaluminum, and water. Polymer Journal, Volume 5, page 231 (1973) discloses a process for preparing binary cis-1,4-/1,2-polybutadiene by polymerizing 1,3-butadiene in the presence of one of the four catalyst systems: (1) a catalyst system comprising dialkoxy molybdenum trichloride and trialkylaluminum, (2) a catalyst system comprising molybdenum pentachloride and triethylaluminum, (3) a catalyst system comprising dioxo molybdenum bis(acetylacetonate) and diethylaluminum chloride, and (4) a catalyst system comprising dioxo molybdenum bis(acetylacetonate), triethylaluminum, and a halogen compound such as ethylaluminum dichloride, carbon tetrabromide, t-butyl chloride, or iodine. U.S. Pat. No. 3,817,968 discloses a method of producing binary cis-1,4-/1,2-polybutadiene by polymerizing 1,3-butadiene in the presence of a catalyst system comprising dialkoxy molybdenum trichloride and trialkylaluminum, or a catalyst system comprising dioxo molybdenum bis(acetylacetonate) and dialkylaluminum chloride. Journal of Molecular Catalysis, Volume 17, page 65 (1982) discloses a process that produces binary cis-1,4-/1,2-polybutadiene by polymerizing 1,3-butadiene in the presence of a catalyst system comprising iron tris(acetylacetonate), triisobutylaluminum, and 1,10-phenanthroline. All of the aforementioned catalyst systems, however, have very low activity and therefore have no industrial utility.
Because binary cis-1,4-/1,2-polybutadiene is useful and the catalyst systems known heretofore in the art have various shortcomings, it would be advantageous to develop a new and significantly improved catalysts that have high catalytic activity and stereoselectivity for polymerizing 1,3-butadiene into binary cis-1,4-/1,2-polybutadiene.